Luminescent tube system and apparatus



June 2G, w44. C, R BOUCHR ET AL 2,351,915

LUMINESCENT TUBE SYSTEM AND APPARATUS Filed July 14, 1941 2 Sheets-Sheet l Q6 j MJ j j@ ji j@ jl? 512 m5,@

fva/f/vra June 20, 1944.

C. P. BOUCHER ET AL LUMINESCENT TUBE SYSTEM AND APPARATUS Filed July 14, 1941 Kyi-g 52 as f2@ 2 Sheets-Sheet 2 diff Patented June 20, 1944 LUMINESCENT TUBE SYSTEM AND APPARATUS Charles Philippe Bouclier, Paterson, and Frederick August Kuhl, Ridgewood, N. J., asslgnors .to Boucher Inventions, Ltd., Washington, D. C.,

a corporation of Delaware Application July 14, 1941, Serial No. 402,413

9 Claims.

Our invention relates to fluorescent gas discharge tube lighting systems, and more particularly concerns various features of safety in connection therewith.

An object of our invention, therefore, is to produce a fluorescent gas discharge tube lighting system, including a high leakage reactance autotransformer and hot-cathode fluorescent tubes functioning on cold-cathode operation, having safe operating characteristics upon either failure or removal of a tube from thesystem.

Another object is to produce a fluorescent gas discharge lighting system employing a high leakage reactance autotransformer, characterized by its safety under all operating conditions', and by freedom from overvoltage upon tube failure, and

by deenergization of part or all of the auto-' transformer upon removal of one or, more tubes from the system.

A further important object is to produce a socket for use in the above-described system capable of facilitating the results set forth in the foregoing.

Other objects in part will be obvious and in part pointed out hereinafter.

Our invention accordingly consists in the various elements and features of construction, and in the relation of each of the same to one or more of the others, all as pointed out hereinafter, and the scope of the application of which is set forth in the appended claims.

Referring now to the. drawings, wherein are disclosed certain illustrative embodiments of the present preferred forms of our invention, Figure l depicts in schematic elevation a form of our invention wherein the energizing supply source is connected across the terminals of the several fluorescent tubes at points within the several branches of-the energizing circuit for the primary coils.

Figure 2 discloses in schematic elevation an autotransformer somewhat similar to that illustrated in Figure l and having double circuits, together with the related details of the system, but in which the leads of the primary energy source are series-connected across the terminals of the hot-cathode tubes, and in which a cutout relay is provided as an auxiliary load across each secondary coil.

Figure 3 is a schematic view of the electrical part of a third embodiment in which for clarity the transformer core is omitted, inasmuch as the core design is substantially that illustrated the terminals of each of the two hot-cathode tubes.

Figure 4 is a perspective view with parts broken away for clarity of a. socket schematically illustrating certain features of our new invention.

'I'hroughout the drawings, like reference numerals denote like structural parts.

As conducive to a more complete understandlng of our invention, it may be stated at this time that more and more, the exploitation of fluorescent gas discharge tube lighting is encroaching on the field heretofore accepted as constituting the province of conventional incandescent bulb lighting. At the presenttime the acceptance of this new tube lighting is so widespread that it bids fair to replace in large measure such incandescent bulb lighting.

Many reasons readily present themselves as controlling of the rather startling success and acceptance of fluorescent lighting. With no attempt to enumerate all of them, it is interesting to consider but a few of these incidents of practical utility, to permit better comprehension of the reasons dictating the replacement of filamentary lamps vby fluorescent gas discharge tubes.

For example, these tubes have only slightly greater first cost, and both the tubes themselves and the auxiliary equipment necessary for use in connection therewith, have a rated life, usually guaranteed, of at least 21/2 times the life of fllamentary bulbs. Additionally, these tubes have an emission of useful and visible light per` unit of power input which is about 2% times that of the incandescible filamentary bulb. Lamps have been developed in this field and made available on the market, capable of emitting light of various accurately-controlled and pleasing color combinations, hitherto totally unobtainable with the use of the conventional iilamentary bulbs. A wide vista of new modes of utilization is opened due to the considerable length of such tubes and their adaptability to a variety of desired profiles. Because the luminous efficiency of these tubes is greater, the tubes do not give rise to detrimental heating, and the convection and conduction heating which does take place is more readily accommodated by persons in the vicinity of the light sources. Not only do such lamps give rise to more pleasing lighting effects and to more ready accommodation thereof by the users, but as Well, these lamps have been found to be admirably suited ior'floodlighting effects in banks of several tubes. The definite indications are that after certain important constructional and opercertain substantial defects which naturally retard the development of these lighting systems. Thus, for illustrative purposes, attention may be directed to the fact that although these known hot-cathode fluorescent tubes now currently in use have, as described, a greater life span than do the known incandescent bulbs, nevertheless there are serious limitations on that useful life span and theconstruction of those tubes is such that failure may be predicted with reasonable certainty after a predictable period of service. Accordingly, such hot-cathode tubes can be employed only in systems requiring complicated,

4 costly and fragile auxiliary apparatus, thereby increasing the costs, both initially, for installation, and for maintenance. These hot-cathode tube systems are found to be comparatively slow in starting and to be unstable both in striking and in the maintenance of the arc when cold weather conditions prevail. Lastly, any attempt to operate the tubes on currents lower than the values for which the tubes are rated in order to produce light emission of lower intensity, is met with both unstable operation and marked decrease in the life of the filamentary electrodes which form an essential part ofthe known hotcathode tubes.

In our co-pending applications, Serial Nos. 402,410, 402,411 and 402,412, filed July 14, 1941, we have illustrated and described new forms of fluorescent gas discharge tube lighting systems employing high-leakage reactance autotransformers therein and capable of using hot-cathwe have designed for use in connection with sysltems of the types set forth in our said 3o-Dending applications. We accomplish this objective by connecting the leads from the primary source of energy, either before or after those leads are branched to the one or more primary coils, in series across the dual terminals of either one or both hot-cathode fluorescent gas discharge tubes which may be employed inour new electrical systems. This connection of the energy source across the tube may be accomplished illustratively by the use of a specially designed socket, ernploying broadly the constructional features illustrated in Figure 4 herein.

Referring now to the constructional embodil ment disclosed, solely by the way of illustration ode fluorescent tubes on cold-cathode operation.

As disclosed in our said co-pending applications we have discovered that fluorescent lighting systems functioning on cold-cathode operation give rise to many practical and important advantages as contrasted with the conventional hot-cathode operation. We have stated in our co-pending applications Ithat we can employ either fluorescent tubes made up especially for cold-cathode operation, in which case the tubes could be obtainable on special order, or the hotcathode tubes now readily available on the market, these hot-cathode tubes being adapted for cold-cathode operation by short-circuiting the illamentary electrodes thereof.

Among the aforementioned advantages flowing from the cold-cathode operation may be listed the provision of the required high starting voltages with automatic adjustment to the lower operating voltages once the arc across the tube is struck, all in the absence of complicated auxiliary equipment. The separate ballast, starting switch, and compensator heretofore considered necessary are no longer required when recourse is had to our new lighting system. As is fully set forth in our co-pending applications, tubes so operated are quick starting, have long tube life, possess stable starting and operating characteristics during prevailing cold weather, have longer duration of light emission during each half-cycle of energizing current, and will function on dimmer operation, that is, on light emissions lower than that for which the tube is rated.

Our new system has comparatively low current demand, is simple, reliable, compact and extremely sturdy. a

It is the purpose of this application to set forth various important safety features Whih 'l5 and not by way of limitation, in Figure l, we may preface our discussion thereof by calling attention to the fact that the autotransformer according to our invention may have either a single or a double secondary circuit, and the core may be constructed to provide either a single or double magnetic circuit. Furthermore, assuming that the high-leakage reactance transformer is of the double magnetic circuit type, employing two primary coils one in each magnetic circuit, then these primary coils may be connected either in parallel or in series across the source of energy supply.

In the embodiment illustrated in Figure l and now under discussion, we disclose, for purposes of illustration, an autotransformer of the highleakage reactance type having two secondary circuits and constructed to provide two groups of parallel magnetic paths, and in which we connect the two primarycoils in parallel across the source of primary energy.

With the foregoing in mind, we observe that the transformer core consists of a central, longitudinally extending leg I0, of magnetic material, and outer legs II, I2 of like material disposed on opposite sides thereof and extending in spaced relation therewith. Mid core portions MI and M2 and end pieces I3, I3 and Il, Il serve to interconnect magnetically the outer and inner legs near their centers and at their ends, respectively. In this manner the transformer core is divided into two groups of parallel magnetic paths. In the rst group one path is traced up core portion -MI, to the right in Figure 1 along leg II, through first end piece Il, to the left across leg I0, and back to MI, and another path is traced down core portion M2, to the right across leg I2. through the lower end piece Il and to the left across leg I0 back to M2, In the second group of magnetic paths a path may be traced down core portion M2, to the left in Figure 1 along leg I2, up second end piece I3, to the right across leg III, and back to M2, while a second path may be traced up through MI, to the left along leg II, down the upper part of core portion I3 and back across leg I0 to MI. It is apparent, therefore, that these two groups of parallel magnetic paths have a leg in common consisting of the core portions MI, M2 and that portion of central leg III embraced therebetween.

In each group of parallel magnetic paths the mid core portions MI, M2, outer legs II, I2 and end pieces I3, Il and Il, I4, respectively, define a pair of spaces. one on each side of central leg I0. The pair of spaces within each group of magnetic paths is designed to receive the primary and secondary coils for that particular group of magnetic paths. The coils are disposed about central leg I with the primary coils disposed adjacent the common magnetic leg, for reasons which will be more fully developed hereinafter.

In each pair of spaces there extends from the legs II, I2, respectively, between said primary and secondary coils, towards but short of the central leg Ill, intermediate shunts of high reluctance calibrated in accordance with the load for which the transformer is designed. The mid-core portions, end pieces, and intermediate shunts are all formed of magnetic metal.

The construction of the transformer core, except for some minor details which will be pointed out from time to time 'in the following text, is substantially the same in the three illustrative embodiments described in this specification. Accordingly, no attempt will..be made to describe in detail the construction of the transformer core shown in Figure 2, while the transformer core has been entirely omitted in Figure 3.

Thus, in the embodiment according to Figure 1, a primary coil PI and a secondary coil SI are disposed in the pair of spaces provided in the first group of parallel magnetic paths, to the right in Figure 1 of the common magnetic leg. Similarly, a primary coil P2 and a secondary coil S2 are provided in the second group of parallel -magnetic paths to the left in Figure 1 of the common magnetic leg. In each instance it will be seen that the primary coils are adjacent the common magnetic leg while the secondary coils are adjacent the end legs I4, I0, I4 and I3, I0, I3, respectively. Intermediate shunts ShI and Sh2 extend from legs II and I2 respectively between primary and secondary coils PI and SI towards but short of central leg I0. 'I'he shunts ShI Sh2 thus provide between their one ends and the leg I0, air-gaps GI and'GZ of high reluctance calibrated in accordance with the particular load for which the transformer is designed.

In like manner, intermediate shunts Sh3 and Sh4 extend between the secondary coils SI and S2 from outer legs II and I2, respectively, towards but short of central leg I0. They provide therebetween air-gaps G3 and G4 of high reluctance calibrated in accordance with the particular load for which the transformer is designed.

A source of primary energy I5 is adapted to be connected across the primary coils PI, P2. This connection may be either series or parallel. -Series connection provides for a potential drop across each primary coil of but half the total voltage output of the source of energy I5. Thus, for .the same potential drop across each coil for either parallel or series connection thereof, the series connection possesses the advantage that higher service voltages may be employed, with consequent saving in transmission losses. The disadvantage is present, however, that upon failure of either primary coil the associated primary coil likewise becomes deenergized. Where parallel connection of the primary coil is utilized, each coil takes the full potential of the energy source independently of the other coil. In the present embodiment the energy source I5, as has been stated hereinbefore is parallel-connected across primary coils PI, P2.

In this' embodiment, however, before discussing the energizing circuit it will be interesting first to develop the secondary circuits. Thus, secondary coil SI is provided with right and lefthand terminals I6, I'I; primary coil PI with right and left-hand terminals I8, I9; primary coil P2 with right land left-hand terminals 20, 2|; and secondary coil S2 with right and left-hand terminals 22, 23.. In circuit with secondary coil SI is a fluorescent gas discharge tube TI, whilein circuit with secondary coil S2 is a fluorescent gas discharge tube T2. These tubes TI, T2 are of the conventional hot-cathode type which now can readily be obtained on the open market. conventionally they consist of an elongated glass tube containing a. filling of suitable inert gas and a small quantity of mercury and forming a space discharge path and being interiorly coated with a suitable fluorescent salt, the secondary radiation of which is visible and of the desired color. A base is provided at each end of the tube, on which base is mounted a lamentary electrode. 'Iwo terminals. one connected to each end of said nlamentary electrode, project exteriorly from the tube through the corresponding base. These electrodes are intended to be connected across a source of electrical energy. The filamentary electrode serves to prepare the tube for the maintenance of an arc discharge thereacross. Once the arc is struck the filament is taken out of operation and the arc is maintained directly between the spaced electrodes.

Each secondary coil and its associated tube is series-connected across the network consisting of the parallel-connected primary coils PI, P2. Thus for example a circuit may be traced from secondary coil SI, terminal I 6, lead 24, socket 25, across tube TI, to socket 26. From there one branch circuit may be traced from leads 21 and 23 to terminal I 3 of primary coil PI, thence to the right through said primary coil to terminal I8, and thence through lead 29 to terminal I'I and back through secondary coil SI. Another branch circuit may be traced from socket 26 through lead 30 to terminal 2I of primary coil P2, thence to the right in Figure I through primary coil P2, across terminal 20, through leads 3I and 32 to socket 33, and thence through lead 29 and terminal I1 back to secondary coil SI.

At the same time circuits may be traced through the other secondary coil S2 and tube T2 as follows: The rst circuit may be traced from terminal 22 of secondary coil S2 across lead 30 to terminal 2| of primary coil P2, thence to the right in Figure 1 through primary coil P2, down through terminal 20 and leads 3|, 32 to socket 33, thence across tube T2 to socket 34 and back through lead 35, terminal 23 and to the right in Figure 1 across secondary coil S2 to the point of beginning. The other branch of this secondary coil may be traced from terminal 22, across lead 30, socket 26, lleads 21 Iand 28 to terminal I9, to the right in Figure l across primary coil PI down terminal I8, across lead 29, to socket 33, across tube T2 to `socket 34, and back up through lead 35 and terminal 23 to secondary coil S2.

The foregoing circuits have been traced for an assumed half-cycle of current flow. During the next subsequent half-cycle of current flow, the direction of current flow will be just the opposite to that described. I

An important feature of our invention is the design of the sockets for receiving 'the dual terminals of one end of each tube. The sockets 26, and 33 in the embodiment undergoing description are constructed in such `manner that the primary charging circuit for one or both of the primary coils PI, P2 is completed upon insertion of the corresponding tube into its socket, and is broken upon removal o f the tube therefrom. In this manner it is ensured that the primary coil is deenergized upon the removal of the corresponding tube.

With the foregoing in mind, We are now in an advantageous position to discuss the charging circuits rior the two primary coils PI, P2. Let us assume `a halt-cycle in which current riows to the right from energy source ii, up through lead 2l. One branch oi the primary supply network extend through terminal l2, to the right in Figure l through primary, coil Pl back through terminal I8 and lead 2l to socket Il, across that socket to lead 22, and back through lead Il to the left-hand side of the energy source Il. It is especially important to note that this parallel charging circuit includes therein the pair oi' terminals of tube T2 which engage in socket 33. Upon removal of tube T2, accordingly, this branch of the primary network is deenergized,

' and primary coil Pl likewise is deenergized.

The other primary charging circuit can be traced from the right-hand side of energy source I through lead 21, across socket 26 to the terminals of tube Ti, and through lead 30 to terminal 2| of primary coil P2, then down through terminal 2li and-lead 2i back to the left side of energy source i5. Here again the two terminals of tube TI are received in a socket and are included in the circuit energizing primary coil P2. In the alternate half-cycles oi current flow the direction of the primary charging current is .'iust the reverse of that described.

Let us assume that tubes TI and T2 are both inserted in sockets 25, 2B and 3l, Il, respectively, and let us further assume that the switch (not shown) is closed across energy source l5. Both primary coils Pl and P2 are then energized through the circuits previously described. Now let us assume that it is desirable to remove say tube TI. Upon removal of this tube the charging circuit through primary coil P2 is broken at socket 28. due to the i'act that the pair of terminals at the left end of the tube TI are normally included by socket 26 in this charging circuit. Primary coil P2 immediately becomes deenergized. Primary coil Pl, however, remains energized. Since however, the secondary circuit through tube TI is broken by the removal of this tube, there can be no current ilow through the load circuit of secondary coil SI. Similarly, since the return circuit for the tube T2 and secondary coil S2 and including primary coil PI is through the socket 28, and further, since the circuit through this socket is broken upon the removal of the tube TI, it will be seen that the tube T2 likewise is deenergized, upon removal oi' the tube TI.

At this time we will develop for the embodiment undergoing discussion the manner in which the flux courses the several magnetic. paths in the transformer core. Since the coursing oi' ilux is substantially the same in the cases of the embodiments of Figures 2' and 3, and since the principle involved is the same, and further, since the core is not illustrated in Figure 3, discussion of the flux circuits in these two embodiments will be omitted.

While it is possible to connect the primary coils PI, P2 in either aiding relationship on the one hand, or opposed or bucking relationship on the other hand, we are elect for purposes of illustration to show them as connected in bucking or opposed relationship. This gives rise to a slight increase of eillciency, in aiding what may be termed a shift of ilux upon increase in load across one secondary circuit prior to similar rincrease of load in the other secondary circuit. In such a case the flux increases in the magnetic path containing the unloaded secondary circuit. Where the coils are connected in aiding relationship. the midcore portions MI, M2 may be materially reduced in size, or in a number of instances, entirely eliminated.

Assume a momentary half-cycle of current now such that the primary flux generated by the passage of the current through the primary coils is in the direction shown by the arrows in Figure 1. Then discussing the ilrst group of magnetic paths for purposes oi' illustration, the flux coming from coil PI passes to the left in Figure l to the common magnetic leg. 'Ihere it bucks the ilux from coil P2 which tends to flow in the opposite direction'across this leg. Accordingly, the primary flux from coil PI splits into two streams which course in opposite directions along this leg. The outer legs Il and I2 being substantially symmetrical with reference to leg I0, as well as the shunts Shi, Sh2, these two streams oi' ilux are substantially equal. One stream courses up through mid core portion MI and to the right in Figure 1 along legV Il. Choosing the paths of least reluctance, only a very little of the flux courses at this time down through shunt Shl. By far the greater part of the ilux courses to the right along leg Il, and down first end piece Il, to the right-hand end of central leg l0. The other stream of ux courses down through mid core portion M2 and to the right in Figure l along outer leg i2. Likewise choosing the paths of least reluctance, only a very small part of this flux courses along shunt Sh2. By far the larger part thereof courses up through second end piece i4, to the right-hand end of leg l0. The two streams of flux re-unite at central leg lil and the combined stream courses to the left along leg ill to primary coil Pl. In so doing this combined stream interlinks secondary coil Si, and generates therein a high voltage. Inasmuch as the arc load across the secondary coil has not yet been energized, coil Si interposes but little impedance at this time.

At the same time, a similar flux circuit may be traced for the flux from the primary coil P2. Flowing to the right in Figure 1 along central leg I0 from primary coil P2, the primary flux bucks the primary flux from coil PI in the common magnetic leg and splits into two streams. Because oi the symmetry of the two legs Il, I2 as well as the shunts S113, SM, these two streams of flux are substantially equal. One stream courses up core portion Mi and to the left in Figure 1 along leg Ii. Seeking the paths of least reluctance, only a very small part of this ux courses down along shunt Sh3. By far the greater part of the ilux courses to the left across leg 1|, down iirst end piece I3, to the left-hand end of central leg I0. 'I'he two streams of llux re-uniting at leg I0, the combined stream courses to the right in Figure l along leg l0, back to primary coil PZ. During this movement the combined stream of flux interlinks secondary coil S2 and induces a high secondary voltage therein. Inasmuch as the arc load across this secondary coil is not energized, the secondary coil S2 interposes but little impedance at this time.

During the next current half-cycle, the direction of coursing of the flux is just the reverse of that described. Inasmuch as the direction of coursing of the iiux is substantially the same in the two parallel magnetic circuits. it is suillcient for purposes of illustration to describe the direction of reverse coursing for but a single secondary circuit. This will be done in connection with the (primary coil PI -alonglleg Ill, interlinking secondary coil SI and inducing a high secondary voltage therein. At the right-hand end of leg I the ilux splits into two equal streams. One stream courses up through first end piece I4, and

to the left in Figure 1 alongouter leg II. Seeking' the paths of least reluctance, only a very small rise to a. back magnetomotive force in that coil.

part of this flux courses down through shunt Shl. .i

By far the greater part of the iiux continues to the left in Figure. 1 along leg II, and courses down mid core portion MI to central leg I0. Simultaneously the other stream of flux courses down through second end piece I4 and to the left along leg I2. Likewise seeking the paths of least reluctance, only a very small part oi this iiux courses upv through shunt Sh2. By far the greater part of this iiux continues to the left along leg I2 and courses up core portion M2, to central leg I0. The two streams re-unite at leg IU and they course back to primary coil PI. During the next subsequent half-cycle of charging current the path of the ux from primary coil PI is of course just the reverse of that indicated by the arrows in Figure 1.

While the tubes TI and T2 are supposedly of like electrical characteristics, as well as the sockets 25, 26, 33 and 34 and secondary coils SI and S2, nevertheless almost invariably there are some lslight differences in the impedances offered thereby, so that one of the secondary circuits will be found to have a somewhat greater impedance than does the other secondary circuit. The arc is found to strike first across the tube in the circuit of lower impedance. Let us assume that it is the circuit including tube TI and coil SI which has the lower impedance. Accordingly, after the passage of but a comparatively few current cycles, the tube TI, operating with its terminals short-circuited by sockets 25, 26 so that it functions on cold-cathode operation, is brought into a condition of such excitation that the arc strikes thereacross.

Immediately a comparatively large current begins to flow across the tube and its associated secondary coil SI. Because this tube and the corresponding secondary coil are series-connected across the primary network consisting of coils PI and P2, this same increased current flows across that network and, splits inversely in the ratio of the impedances of those two coils, each of which primary network. Since the primary coil PI in-y is disposed in-a separate branch of that' A secondary iiux is developed therein which bucks or opposes primary ilux tending to interlink secondary coli S2.

To develop this phenomenon, let us refer again to the iirst group of magnetic paths, including coils PI, SI and let us trace the coursing of the primary flux.` Assuming current iiow such that the flux courses in the direction of the arrows, then the body of primary ilux lcourses along leg I0 to the lett in Figure 1 from the primary coil PI. Splitting into two equal streams at the common magnetic leg and for the reasons already described, one stream courses up core portion MI and to the right in Figure 1 along leg II. The

flux seeking the paths of least reluctance, only a very small part continues on down through ilrst end piece I4 to the right-hand end of central leg I0 and then back to the left in Figure 1 along that leg to primary coil PI, interiinking coil Si. By far the greater part of this stream of flux courses down through shunt Shl and across air-gap GI to leg I 0. This high reluctance shunt path is now of lower reluctance than is the path interlinking coil SI since this secv ondary now develops a higher counter magnetomotive force due to the energization of the load thereacross. Simultaneously the second stream of magnetic iiux continues down through core portion M2 and to the right in Figure 1 and along leg I2. Only a small part of the flux continues up through second end piece I4 to leg I0 interlinking coil SI and coursing back to the left in Figure I along leg I0 to primary coil PI. By far A the greater part of this flux courses up through shunt Sh2 and across air-gap G2 to central leg I0. The two streams of flux there re-uniting, they course to JVthe left in Figure l along leg I0 back to primary coil Pi, completely shunting or by-passing secondary coil SI. An important feature of the design of this transformer is that the intermediate shunts Shi and Sh2 and their creases in impedance upon striking ofthe load across coil SI, magnetically in circuit therewith, due to itsincrease in inductive reactance, the greater part of the current is impressed across the branch of the primary network which includes primary coil P2. The flux generated depending upon the ampere turns in the primary coils and the number of turns being a constant, the primary flux generated by coil P2 and coursing throughthe second magnetic path increases uponthis increase in charging current.l The increased flux results in the induction of a still higher voltage in secondary coil S2, which is impressed across tube T2. This increased voltage results in almost instantaneous striking of the arc across that tube.

As soon as the arc lis struck across tube T2 and current begins to flow through the corresponding secondary coil, this current fiow gives associated air-gaps GI, G2 have just suflicient reluctance to ensure that enough, but no mo-re than enough, iiux interlinks secondary coil SI -after the load across the latter has been energized, to induce therein a voltage suflicient to support the arc load disposed thereacross.

In the next half-cycle of current flow the direction of coursing is just the reverse of that described. The ilux courses to the4 right in Figure 1 along central leg I0 from the primary coil PI. Only sufiicient flux interlinks coil SI to induce therein the voltage necessary to maintain the arc across tube TI. At the right-hand end oi leg I0 the small part of ilux which interlinks coil SI splits into two streams, one of which ows up along rst end piece I4, through leg iI to the left in Figure l, down core portion MI to leg I0 and back to primary coil PI, while the other stream courses down second end piece i4, along leg I2 to the left in Figure 1, through core portion M2 and leg I0 .back to primary coil PI. By far the greater part of the flux splits into two streams. One stream courses up across air-gap GI, through shunt Shi, to the vleft along leg I I, through core portion MI to leg I0. The other stream courses down across air-gap G2, through shunt SM, to the left along leg I2, up through core portion M2, to leg IIJ.` The two streams of fiuxthere re-uniting, they ow back to right in leg I0 to primary coil PI Since the direction of the coursing of the flux, in the group of parallel magnetic paths embracing the coils PI and SI during such times as the load across secondary coil S2 is energized, is just the same as has been described immediately hereinbefore in connection with the other group parallei magnetic paths, it is unnecessary to trace the coursing of the llux tor this second parallel magnetic path, and such description will be omitted, for simplicity.

While in the embodiment just described, removal of one of the tubes from its sockets will result in deenergization of the primary coil in that branch of the primary network in which the tube is connected, and will result also in the deenerglzation of both tubes, we find that the other primary coil remains enei-gized, and is supplying a reduced quantity of flux to both secondary coils. Inasmuch as the secondary circuit including the tube which has not yet been removed is broken by the removal of the one tube, however, the remaining tube is deenergized. The coursing of the ilux from that primary coil which remains energized, however, gives rise to an induced voltage in the secondary coil which was in circuit with the tube which was removed, so that the open sockets cooperating with that tube will be at the comparatively high potential induced in the corresponding secondary coil and thus represent a source of potential hazard, should accidental contact be made thereacross.

It is the purpose of the embodiment according to our Figure 2, which will now be described, to eliminate even this slight and rather remote danger. Therein the leads 28 and 3l from the source of primary energy i5 are connected across the socket of tubes TI and T2 at points before the leads are branched of! to the respective primary coils. The removal of either tube, therefore, is followed by complete deenergization of the entire system. This can be demonstrated by tracing the primary circuits.

Assuming a momentary current flow such that the current flows to the right in Figure 2 from the supply source I5, then a circuit can be traced through lead 28 to socket 26, across the terminals at the corresponding end of the hot-cathode tube TI, thence through lead 28 to junction 33. From junction 36 one branch extends through lead 31 and terminal 2l, to the right in Figure 2 through primary coil P2 to terminal 28, and thence through lead 3l, socket 33, across the paired terminals of the corresponding end of the hot-cathode tube T2, and thence through lead 3l back .to the left-hand side of energy source l5. The other parallel branch of thisl primary network can be traced from junction 36 to terminal I3, thence to the right in Figure 1 through primary coil Pl, down across terminal I8 and through lead 38 to junction 38, thence' through lead 3l to socket 33, across the paired terminals of the corresponding end of the hotcathode tube T2, and back through lead 3| to the left-hand side of energy source l5. During the next half-cycle of the current iiow, of course, the direction of the coursing of the current is exactly the opposite of that just traced. The primary coils PI, P2 are connected in opposed relationship and the construction of the core follows the same teachings as have been described hereinbefore in connection with Figure l. Thus the coursing of the flux through the several magnetic paths and upon the occurrence of the various phenomena there described is Just the same as has already been narrated. Repetition is unnecessary at this point.

The secondary coil electrical circuits may be traced as follows: One such circuit extends from the right-hand terminal I6 of secondary coil Si, through lead 24 to socket 25, across tube TI to socket 26, through lead 28 to junction 36. The other leg ci this circuit can be traced along leithand terminal l1 oi secondary coil Si and lead 33 to junction 40. From junction 3B one branch circuit may be traced through lead 31, left-hand terminal 2i of primary coil P2, through primary coil P2 to the vright in Figure 2, to terminal 28, thence to junction 39 and back across lead 38 past junction 40 to the left-handterrninal I1 of secondary coil Si. A similar parallel circuit can be traced froml junction 3B, through left-hand terminal I8, to the right in Figure 2 across primary coil PI, thence down right-hand terminal i8 to junction lll and back to secondary coilSi. A

A similar secondary circuit may be traced from right-hand lead 22 of secondary coil S2, and across lead 31 to junctionll. The other leg of this secondary circuit may 'ce traced from the left-hand terminal 23 of secondary coil S2, through lead 35 to socket 34, across tube T2 to socket 33 and up lead 3l to junction 39. From junction li one branch circuit may be traced through left-hand terminal 2i, through primary coil P2 to the right in Figure 2, and along righthand terminal 20, back to junction 39. A similar branch may be traced from junction 4I through lead 31, junction 36, left-hand terminal i8, through primary coil PI to the right in Figure 2, right-hand terminal I8, junction 4U and back through lead 38 to junction 39. OI course during the next subsequent half-cycle of the charging current, the direction oi current flow is just the reverse of that described.

The important part about this construction is that upon removal of either tube from its sockets, open-circuit conditions maintain in one of the primary leads from the energy source l5, so that the entire system becomes deenergized. It isA further to be noted that because the primary coils are deenergized, then upon removal of a tube no high potential secondary voltage is impressed across the corresponding tube sockets. Thus all hazards otherwise attendant upon removal of a tube from the system are substan tially eliminated.

A further reiinement according to our invention is illustrated in this figure, and relates to the provision of a cutout relay across each secondary coil, these relays having impedance characteristics such that they do not come into operation during the normal -functioning of the tube lighting system, and are energized only upon :failure of the tube in the circuit of the corresponding secondary coil.

We nd that when one of the tubes fails, thereby discontinuing the development of appreciable secondary current by the corresponding secondary coil, the quantity of primary flux coursing through this secondary coil induces therein a high open-circuit voltage. While the secondary coil can withstand this high voltage for the comparatively short space of time required to strike initially the arc across the corresponding tube, this elevated voltage represents a source of danger where it endures for any appreciable period of time.

Accordingly, We provide a cutout relay across each secondary coil, which is insensitive to the normal operating voltage of the coils, and which has such inertia characteristics that it does not attract its associated armature for some little time after the high voltage conditions are first initiated. Thus these relays do not come into operation during the starting period. It is quite possible to design the relay in such manner that there is no danger of their cutting in, even during comparative sluggish operation under cold weather conditions.

Thus, amature coil 42 is inserted `by leads 43,

i 44 and 45, 46 across secondary coil Sl. In the ever, and prior to removal of this tube from the system, as forexample when a. tube fails during unattended night illumination and the high voltage current then induced in secondary coil Si endures for a considerable length of time, coil 42 is energized sufficiently to attract armature 46 against terminal 50 and hold it there, thus com pleting a circuit from coil SI through the resistor 48. This resistor is designed to have a reactance corresponding t that of the tube load.

Similarly, a relay coil l is connected by leads 52, 53 and 54, 55 across secondary coil S2. A resistoi` 56 is inserted in a lead 51 forming a continuation of lead 5; Armature 58 coacts with coil 5l and is associated with a terminal 59 of lead 51. The operation is exactly the same as has been described immediately in the foregoing in connection with relay 42 and need not be repeated at this point. l'

All danger of damage to the transformer upon failure of a tube is eliminated` The system can continue in operation on the other tube without detrimental result from the electrical standpoint.

The system according to Figure 3, as already pointed out, employs generally the same high leakage reactance transformer core as has been described hereinbefore with respect to Figures 1 and 2. Repetition of this description therefore becomes unnecessary at this point. Accordingly, both illustration and description of the trans- :former core has been entirely omitted with reference to the embodiment according to Figure 8, it being understood, however, that the design of the core in large measure follows the teachings set forth hereinbefore with reference to Figures 1 and 2.

The electrical circuits of the system according to Figure 3 are in large part patterned after those depicted in Figure 2. Hot-cathode tubes are similarly employed on cold-cathode operation, and advantage taken of details of construction of those hot-cathode tubes to give rise to certain features of safety forming the subject matter of this invention. The important demarcation exists between-the construction according to the present embodiment, however, and that of Figure 2 in that in the instant case, a single lead from the primary source of electrical energy is seriesconnected, before it reaches the parallel-connected network for energizing the primary coils,

across the paired terminals of not one, but both hot-cathode ltubes employed. The other lead from the primary source may be connected directly to the secondary coil network.

It may be briefly stated that this embodiment employs a transformer having two groups of magnetic paths, with two sets of windings, one set in each group of magnetic paths, and each set consisting of a primary and a secondary coil. The primary coils are connected in parallelopposed relation across an energy source; and each secondary coil, together with a series-connected tube load, is inserted in series across the network consisting of the parallel-connected primary coils.

Thus primary coils PI and P2 are connected in parallel-opposed relation across a source of alterating-current electrical supply l5. Secondary coils SI and S2 each have a hot-cathode ucrescent gas discharge tube TI and T2, respectively, series-connected thereacross vfor functioning on cold-cathode operation. Sockets adapted to short-circuit the paired terminals of the hotcathode tubes serve to condition thesetubes for the desired cold-cathode operation. These tubes TI and T2 are of the same hot-cathode fluorescent gas discharge type previously described. They consist ofl glass tubular walls, lined with fluorescent salts, and contain a filling of suitable inert gas, and a drop of mercury. Paired electrodes extend exteriorly from fllamentary electrodes at each endof the tube.

Thus, for a given half-cycle of current flow, a circuit may be traced from the energy vsource I5, to the left in Figure 3, up lead to junction 6|.

One branch of the parallel network can then be traced up lead 62, to the left in Figure 3 across primary coilP2, down lead 63 to junction 64. Thence a return circuit may be traced through lead 65, across socket 25 of tube TI, through lead 56 to socket 33 of tube T2, and through lead 61 to the right-handlside of energy source. Similarly, another branch charging circuit simultaneously exists, traced from junction 6l, across lead 68 to the right in Figure 3, up lead 69, across primary coil Pl to the left in Figure 3, and down through lead 10 to junctionv 64. During the next half-cycle of current ow the coursing of the circuit is `just the reverse of that described.

Upon removal of either tube it will be noted that the primary energizing circuit is broken, thus deenergizing both primary coils. Thus upon removal of tube Tl from its sockets, the primary circuit is broken at socket 25, while upon removal of tube T2 from its sockets, this same primary circuit is broken at socket 33. .Both primary coils become deenergized, and the secondary system is completely dead.

Secondary circuits energized by potentials induced in each secondary coil, each include a corresponding space discharge tube Tl and T2, and are series-connected across the primary network. One such secondary tube circuit may be traced, for an assumed half-cycle, from the end of secondary vcoil SI at the right in Figure 3, through lead 1| to socket 26, across tube Tl, socket 25, and lead to junction 64. Another leg of this circuit may be traced from the lefthand end of secondary coil Si, down through lead 'l2 to junction 13. From junction 54 one branch may be traced through lead 63, to the right in Figure 3 across primary coil P2, down through lead 62, junction 6I and lead 68 to junction 13. The other branch may be traced simultaneously from junction 64, lead 10, to the right in Figure 3 through primary coil PI, and down through lead 69 to junction 13.

Similarly, a corresponding set of circuits may be traced for simultaneous current flow through secondary coil S2 and tube T2. From the end of coil S2 at the right in Figure 3, current flows through lead 14,` socket 34, tube T2, socket 33, lead 66, across socket 25 and lead 65 to junction 64. The other left of this circuit includes the During the next half-cycle of current fiow'f" of course, the direction in which the current traverses these circuits is exactly the opposite of those traced. The polarity is reversed.

While as suggested, the sockets which can be y utilized in connection with our invention can assume any of a number of different structural embodiments, we illustratively disclose a satis factory example of such socket in Figure 4. The essential requirement of such socket is that the sleeves for receiving the terminals of the corresponding tube be provided with a short-circuiting jumper extending therebetween, and through which jumper a circuit is completed only upon insertion of the tube terminals in those sockets.

Referring to Figure 4, the socket pictured therein solely by way of illustration consists of an outer shell 1B which conveniently may be of metal of other suitable material. Disposed within the cylindrical shell 1G are tubular sleeves11, 18, paired to receive the extending terminals which are disposed at one end of a fluorescent gas discharge tube, and formed of suitable insulating material, such as rubber, molded plastic, or the like. In any desired manner these sleeves are spaced from the shell 16, as by the introduction of a suitable cement filler or the like. A metal Jumper 19 extends between the sleeves 11, 1l, and presents a metallic bearing surface on the interior of those sleeves. Leads 80 and 8| extend from the interior of the respective tubular sleeves to the exterior of the shell 16, preferably rearwardly or laterally, and are intended to be connected in the electrical circuit with which the socket is associated, thus completing a circuit across said metal jumper when a tube is inserted in the socket. Should the particular socket 16 be intended for use at that end of an associated tube which has only one current lead, then the leads 80 and 8| are preferably connected together for purposes of safety,

since both leads would be at the same potential, and the ioined leads are then connected in an electrical circuit.

The several features of safety forming the subject matter of this' invention permit us to operate our high voltage, cold-cathode fluorescent gas discharge systems without danger resulting from either failure or removal of. one or more tubes forming part of the lighting system. Upon removal of a tube according to the embodiment of Figure l, one of the primary coils is deenergized, and the remaining tube is likewise deenergized. In the embodiment according to Figures 2 and 3 removal of those tubes is attended by deenergization of both primary coils. Further, as we illustrate in connection with Figure 2, failure of one of those tubes, which nevertheless is physically retained in the system, is attended by the automatic establishment of a shunt circuit through a relay-controlled branch, with attendant assurance that no detrimental high voltages will maintain in the circuit.

We claim:

1, A fluorescent gas discharge tube lighting system comprising, a transformer having a primary winding and secondary winding; a fluorescent tube; a pair of sockets into which said tube is positioned connected to said secondary winding; and connections between the primary winding and a source of alternating current electrical energy by way of at least one of said pair oi tube sockets with its terminals connected in series. therewith, said one socket being so con structed that insertion of the tube short-circuits the socket terminals and removal of the 'tube therefrom interrupts the circuit source to the primary winding.

2. A fluorescent gas discharge tube lighting system comprising, a transformer having two groups of windings each including a primary winding and a secondary winding with the primary windings connected together, two fiuores cent lighting tubes individually corresponding to the groups of windings, a pair of sockets asso ciated with each tube, and electrical connections between the transformer and sockets, with the terminals of at least one ci' said sockets in series with one primary winding so that insertion of its associated tube completes the circuit through said primary winding and removal of the tube cleanerw gizes the primary windings of both groups by interrupting the connections thereto.

3. A fluorescent gas discharge tube lighting system comprising, an autotransiormer having a primary winding and secondary winding, the primary winding being connected across a source 0i alternating current electrical energy; and two fluorescent lighting tubes mounted in two pairs of sockets corresponding thereto, the pairs being individually connected in secondary circuits with the autotransformer, and at least one socket of each pair being serially connected between the transformer and source of supply energy so that insertion of the related tube short-circuits the terminals of the socket and removal of the tube interrupts the circuit source to the primary winding.

4. A fluorescent gas discharge tube -lighting system comprising, a transformer having a primary winding and two secondary windings, the primary winding being connected across a source of alternating current electrical energy; and two fluorescent lighting tubes with their tube terminals mounted in two series of sockets individually corresponding thereto, the pairs being individually connected in secondary circuits with the secondary windings, and at least one socket of each pair being serially connected between the transformer and source and so constructed as to complete the circuit through the socket by way of short-circuiting the terminals of the one associated end of the related tube.

5. A fluorescent gas discharge tube lighting system comprising, a transformer having a pri? mary winding and two secondary windings, two fluorescent lighting tubes individually corresponding to the secondary windings, and sockets into which the terminals of said tubes are positioned connected to said secondary windings, at least one of said sockets being also connected serially with the primary winding and being so constructed as to effect a short-circuit across tube terminals upon insertion of the associated tube to complete the primary circuit and upon removal of the tube open the primary circuit and deenergize the secondary winding corresponding to the other tube.

6. A fluorescent gas discharge tube lighting system comprising, an autotransformer having a primary winding and two secondary windings.

' pletes the primary and secondary circuits and removal of the tube opens the primary circuit and deenergises the secondary winding corresponding to the other tube.

'1. A fluorescent tube illumination system comprising a high leakage reactance autotransformer having groups of parallel magnetic' paths and paired primary and secondary coils in each group of magnetic paths. the primary coil being adapted to be connected across a source of alternating electrical energy, and the secondary coils being series-connected across said primary coils and each being adapted to energize a series-connected fluorescent tube. and a cutout relay and high resistance load controlled thereby substantially equivalent to the associated tube load and branched across each secondary coil and having electrical characteristics such that it comes into operation to shunt said secondary coil with said high resistance upon over-voltage attendant upon failure of the tube load energized by the associl atedsecondary coil, whereby balanced operation of said transformer is preserved.

8. A gas discharge tube lighting system oomprising. a transformer having a primary winding and two secondary windings. two lighting tubes individually connected in circuits with the secondary windings, and delayed-action high voltage control means electrically connected with the secondary windings and actuating a resistance element substantially. equivalent to the tube load so as to shunt said resistanceacross a secondary winding and prevent over-voltage therein attendant upon tube failure, and whereby balancedl operation of said transformer is preserved.

9. A gas discharge tube lighting system comprising. an autotransformer having a primary winding and two secondary windings, two lighting tubes individually connected in circuits with the secondary windings. and delayed-action high voltage controls. each comprising a relay actuating a high resistance shunt circuit substantially equivalent to the tube load and individually connecd electrically with the 'secondary windings so as to shunt a resistance across the associated secondary winding and prevent overfvoltage therein attendant upon tube failure, and whereby balanced operation oi said transformer is preserved.

`CHARLES PHILIPPE BOUCHER..

FREDERICK AUGUST KUHL. 

